This invention relates to the production of dihydric phenols by the oxidation of dialkylbenzenes to dialkylbenzene dihydroperoxides and the acid-catalyzed rearrangement of the dihydroperoxides to the dihydric phenol.
It is known to oxidize meta and paradiisopropylbenzene to meta and para-diisopropylbenzene dihydroperoxide, and to rearrange the dihydroperoxide by acid cleavage (Hock splitting) resorcinol or hydroquinone. See for example Tanaka, et al U.S. Pat. No. 4,049,723, incorporated herein by reference for all purposes, the references disclosed therein, U.S. Pat. Nos. 4,053,520 and 3,968,171 and the paper by J. Ewers, H. W. Voges and G. Maleck entitled "Process for the Production of Hydroquinone", Erdoel Kohle Erdgas, Petrochem. Br. Chem., Vol. 28, No. 1, 1975, pp. 34+.
In the first step of the process, the dialkylbenzene is oxidized with oxygen to dialkylbenzene monohydroperoxide, e.g. para-diisopropyl-benzene monohydroperoxide, which is further oxidized to the dihydroperoxide. In this step the hydroperoxide groups are decomposed in various degrees which gives rise to several by-products including alcoholic and ketonic decomposition products and their further oxidation products. The main by-product is the hydroxyhydroperoxide which results from the oxidation of monocarbinol which itself results from the decomposition of the monohydroperoxide. Thus the process is optimized by choosing the reaction conditions to minimize the production of the hydroxyhydroperoxide. Elevation of the reaction temperature increases the production of the dihydroperoxide and the hydroxyhydroperoxide. However, the production of the hydroxyhydroperoxide increases at a greater rate with an increase in temperature. Thus the reaction is generally conducted at a temperature in the range from about 83.degree. C. to about 87.degree. C. in order to insure good dihydroperoxide yield and to minimize the reactor space required.
Using air as the oxidizing gas, generally the oxygen content of the exhaust gas from the reactor is kept below about 8% for safety reasons. This allows sufficient oxygen to be present in the reaction liquid such that the rate of oxidation is independent of the oxygen content in the liquid and thus is maximal. Formic acid is formed as a by-product of the reaction. Thus the oxidation is carried out in a weakly alkaline range. Low concentration sodium hydroxide, 0.3%, is added to the oxidizer with the oxidate to maintain the pH in the oxidizer from about 7.0 to about 7.5. The pH must be carefully controlled otherwise decomposition reactions are catalyzed increasing the concentration of by-products.
In the second step of the process, the aqueous caustic waste stream is separated from the organic oxidate stream after oxidation.
In the third step of the process, the organic oxidate is extracted with 4% by weight aqueous sodium hydroxide solution. In this step the dihydroperoxide and the hydroxyhydroperoxide enter the aqueous phase, together with other by-products, and unreacted dialkylbenzene, e.g. p-diisopropylbenzene, and monohydroperoxide is recovered for recycling to the oxidizer. Before recycling, however, entrained sodium hydroxide must be removed to insure adequate pH control in the oxidizer. Generally, this is accomplished by subjecting the recycle oxidate to the action of carbon dioxide and several subsequent water washes.
The fourth step of the process comprises transfer of the organic components in the 4% aqueous caustic solution into an organic solvent such as methyl isobutyl ketone and recycling the caustic solution.
The fifth step in the process comprises the acid-cataylzed splitting of the diisopropylbenzene dihydroperoxide, in the organic solvent, to the dihydric phenol and acetone.
The sixth step in the process comprises the separation and recovery of the dihydric phenol from the by-products and organic solvent.
The aqueous caustic waste stream separated from the oxidate in step two contains organic impurities and the desired intermediate, meta or paradiisopropylbenzene dihydroperoxide. These impurities result in a loss of product, and further processing is required to render the waste stream environmentally safe for disposal.